Fix int overflow on x32 processors causing panic (#3810)

During the roll, "duration" is converted to int, causing overflow on x32 processors. The value may be very small or negative, causing a panic in rand.Intn.

app/observatory/burst/healthping.go

@@ -156,7 +156,7 @@ func (h *HealthPing) doCheck(tags []string, duration time.Duration, rounds int)
 		for i := 0; i < rounds; i++ {
 			delay := time.Duration(0)
 			if duration > 0 {
-				delay = time.Duration(dice.Roll(int(duration)))
+				delay = time.Duration(dice.RollInt63n(int64(duration)))
 			}
 			time.AfterFunc(delay, func() {
 				errors.LogDebug(h.ctx, "checking ", handler)

common/dice/dice.go

@@ -14,6 +14,14 @@ func Roll(n int) int {
 	return rand.Intn(n)
 }
 
+// RollInt63n returns a non-negative number between 0 (inclusive) and n (exclusive).
+func RollInt63n(n int64) int64 {
+	if n == 1 {
+		return 0
+	}
+	return rand.Int63n(n)
+}
+
 // Roll returns a non-negative number between 0 (inclusive) and n (exclusive).
 func RollDeterministic(n int, seed int64) int {
 	if n == 1 {